The present invention relates generally to an elevator system and particularly to a belt-like transmission means.
Elevator systems of this kind usually comprise an elevator car, which is movable in an elevator shaft or freely along guide equipment. For producing the movement the elevator system comprises a drive which cooperates with the elevator car and a compensating weight (also termed counterweight) by way of transmission means.
Distinction is made between elevator systems in which steel cables of round cross-section are used as transmission means and more modern elevator systems that have flat belts as transmission means.
An example of an elevator system with flat transmission means is shown in PCT Patent Application WO 99/43602. The elevator car according to this patent application is moved by a drive that is seated at the compensating weight and moves together with the weight.
The described system has the disadvantage that the belt used as the transmission means does not have the optimum traction behavior achievable with specific other belt-like transmission means and that the supply of energy to the drive motor, as also the transmission of signals from associated control and regulating devices, has to take place by way of long, flexible cables.
A further elevator system with a cogged-belt-like transmission means is shown in PCT Patent Application WO 99/43592. In the described arrangement the drive is integrated in the counterweight and a cogged-belt-like transmission means fixed in the elevator shaft serves for transmission of the drive force between counterweight and elevator shaft. Since the elevator car and the compensating weight hang at an actual support means separate from the mentioned cogged-belt-like transmission means; the drive and transmission means transmit only the force difference between the counterweight and the weight of the elevator car.
This system has the same disadvantages as that described in the foregoing and has the additional disadvantage that a cogged belt is used for the drive function and a different means for the support function. By comparison with a system in which the drive function and support function are effected by the same means, in this system there is also required a greater number of rollers or pulleys.
Another form of elevator system with a cogged-belt-like transmission means is shown in U.S. Pat. No. 5,191,920. In the illustrated elevator system the cogged-belt-like transmission means is stationary in the elevator shaft. The drive unit is disposed at the elevator car or at the so-termed load receiving means.
This system therefore has the same disadvantages as described in WO 99/43602. An additional disadvantage here is that due to the elevator drive the weight of the load receiving means and thus the drive power required are increased.
The belts disclosed in the above-identified documents have specific disadvantages. Flat belts have, in elevator equipment with elevator cars which are light by comparison with the useful load, an insufficient traction capability. In the case of cogged belts the problem exists that these do not slip on the drive pulley when the elevator car or the counterweight rests, as a consequence of a control breakdown, on their end position buffers. Moreover, centering of the belt on the belt pulleys cannot be realized without problems. In a given case special measures have to be undertaken at the pulleys in order to prevent the belt from running out of the central position.